Under light-duty driving, the progressive rate springs soak up the small bumps as a softer spring would, but when the conditions get rough and the jumps get big, the progressive rate springs step up to the challenge by getting firmer as the suspension is compressed. This resists the chassis from bottoming out from jumps to keep the chassis under control.

I just installed these on my old emaxx, they went on a set of big bore shocks, they seem to be able to hold up the heavy truck better than the stockers, I've added a bunch of metal parts because if you're not breaking it you're not driving hard enough but they are bigger in diameter than the stock springs and don't sit in the spring cups just right, they hang over a little, they don't seem to be able to fall off but still not a perfect fit, funny seeings how they are both traxxas parts.